IDEC 151 is a primate/human hybrid antibody that reacts with the CD4 antigen or lymphocyte. Unlike other anti-CD4 antibodies which depletes CD4 lymphocyte, IDEC 151 is a non-depleting antibody which interferes with CD4 and R cell function. The study goals are to learn the safety and tolerance of the antibody, to measure the effect of IDEC 151 on the CD4 antigen and to select the dose for expanded clinical trial to be done in the future. A secondary objective is to determine the effectiveness of IDEC 151 in Rheumatoid Arthritis.